This invention relates to apparatus for detecting changes in conditions; particularly but not exclusively to apparatus for determining temperature and/or pressure changes; and especially changes in conditions in items, and for example in big end bearings for internal combustion engines.
In an internal combustion engine, problems can be encountered with the big end bearing overheating which can lead to the engine seizing up. This may occur due to low oil pressure in the bearing. It is generally difficult to detect this overheating due to the movement of the big end, and particularly in larger engines as used in marine applications or power generation.
According to one aspect of this invention there is provided an apparatus for determining a change in a condition in an item, the apparatus comprising a reactive means arranged to react to a change in a condition so as to move a detectable part in one of two directions dependent on the sense in which the condition changes, and a detection means arranged to sense the detectable part when in a predetermined proximal range, the reactive means being mountable on an item, such that when the condition is below a predetermined level the detectable part will be in a position to be sensed by the detection means, but when above the predetermined level the detectable part will not be detected by the detection means, or vice-versa.
In a preferred embodiment, the apparatus comprises a first member comprising the reactive means and a second member comprising the detection means, the first member being mountable on the item and the second member being mountable in a location spaced from the first member. In this embodiment, the detectable part constitutes a part of the first member, and movement of the reactive means moves the part towards or away from the detection means.
The reactive means may be thermally reactive, and preferably comprises an element of a material, and suitably a metallic material, which expands on heating and contracts on cooling. Alternatively, the thermally reactive means may comprise an element of a thermoplastic material which expands on heating. In such case, the expandable element would not contract on cooling, and is preferably replaceable after each expansion.
Where the thermally reactive means comprises an element of a metallic material, the element may be a bimetallic member, for example a bimetallic strip or a bimetallic washer which changes shape upon heating. Alternatively, the thermally reactive means may comprise an element in the form of a shape memory metal. Where the thermally reactive means comprises a bimetallic washer, the first member may comprise one or more domed bimetallic washers which flatten upon heating.
In a further embodiment, the thermally reactive means may comprise a housing containing a fluid which expands on heating. The housing may be provided with a piston adapted to be moved to the expanded condition on expansion of the fluid under the action of heat. Alternatively the housing may be expandable, and may be in the form of bellows.
In a still further embodiment the reactive means may comprise a thermally expandable fluid in a closed channel which channel is provided in a shaped member, such that a change in temperature causes a change in volume of the fluid which causes the shape of the member to change.
The channel may have a sensing portion, which may be spaced from the shaped member, which sensing portion is locatable at the location where conditions are to be monitored.
The shaped member may have a substantially S-shaped or C-shaped profile. The fluid in the channel preferably has a substantially linear thermal expansion, and may comprise xylene.
Alternatively or in addition, the reactive means may be reactive to pressure and may comprise a sprung member or housing in communication with an area where conditions are being monitored, such that increased pressure causes outward movement of the sprung member, or expansion of the housing.
The item may be capable of motion, and preferably rotational or reciprocal motion, such that reaction of the reactive means can bring the detectable part into or out of a detectable position intermittently, on each stroke of the reciprocating motion, or each rotation of the rotational motion. Alternatively, the item can be stationary such that reaction of the reactive means can bring the detectable part of the first member into or out of a continuously detectable position.
The first member may comprise resilient urging means acting against the reactive means. The use of the resilient urging means is particularly suitable when the item is capable of motion, particularly rotational or reciprocating motions, to prevent movement of the detectable part due solely to motion of the first member. The resilient urging means may be a spring, for example a compression spring.
The first member may comprise a securing portion enabling the first member to be secured to the item. The resilient urging means may be arranged in a space defined in the securing portion. The securing portion is preferably provided with a securing formation, e.g. a thread, cooperable with a corresponding formation on the item. Preferably, the securing portion is adapted to be screwed into a threaded core defined in the item.
The securing portion may define a space in which the resilient urging means is arranged. An elongate rod may extend through said space and is preferably attached to the reactive means towards one end thereof and also to the resilient urging means.
An iron containing member or a permanent magnetic member is preferably provided on the rod adjacent the one end thereof.
Alternatively, the reactive means may be mounted to a pivoted member on one side of the pivot with a equaliser member on the opposite side of the pivot, such that the reactive means causes pivoting of the member in response to a change in condition, but the equaliser member substantialy prevents pivotal movement of the member due to movement of the reactive means and/or the item as a whole.
The equaliser member may be arranged to substantially prevent pivotal movement of the member due to ambient temperature changes at the reactive means.
The equaliser member may be substantially physically equivalent to the reactive means to provide a substantially equal resistance to pivotal movement of the member.
Where the reactive means comprises a closed channel in a shaped member, the equaliser member may also incorporate a closed member, which may be filled with a fluid.
Where the reactive means comprises a metallic material element, the equaliser member may be arranged to operate in an opposite direction to the reactive means, to double the effect.
Preferably the equaliser member provides a substantially equal resistive force to the pivoted member as provided by the reactive means. Desirably the equaliser member has a substantially equal mass to the reactive means.
Alternatively, the equaliser member may have a different form to the reactive means.
A detectable part may be provided on the member on each side of the pivot.
The detection means may comprise any sensor suitable for sensing the proximity of an article, for example, a Hall effect sensor or a proximity switch, or a mechanical switch which may comprise a micro switch. The second member is preferably provided with a suitable formation to mount-the second member in the said location. The formations may be in the form of a thread.
The invention further-provides apparatus for detecting overheating-of a big end bearing in an internal combustion engine, the apparatus being according to any of the preceding twelve paragraphs.